In terms of computational power, real computers (ignoring physics) are linear bounded automata, which is a class of automata strictly weaker than Turing machines. Throwing physics into the mix means they’re unreliable computing devices.
No, you’re still limited by the computational power of the universe. Since there is a finite amount of energy and a finite number of particles, you’re limited to a finite number of states. The entire universe is no more powerful than a very large, but finite, linear bounded automation.
